It is often necessary in treating patients to analyze urine specimens to measure the presence and content of various analytes as an indication of the patient's condition, metabolism, and organ function. By way of example, there is a frequent need to test urine specimens from patients as a means of identifying vitamin B.sub.12 deficiency. Up to seven percent of individuals over the age of 65 may have a deficiency in vitamin B.sub.12. If this deficiency is not identified and treated, it can lead to dementia and/or nerve paralysis. A deficiency in vitamin B.sub.12 can be identified by a high urinary methylmalonic acid (MMA) level. If a high urinary MMA level is detected early on, the patient can be treated with vitamin B.sub.12 injections to reduce or eliminate the risks of the condition. Because of the significant pool of individuals who are at risk, there is a need to rapidly test a large number of specimens.
Current methods of urinalysis involve preparation of an individual specimen, followed by introduction of a sample from the prepared specimen into a gas chromatography column. The specimen is introduced at an initial low temperature, after which the temperature of the column is raised in accordance with a predetermined instrument program. The specimen is volatilized and is carried through the column with a gaseous carrier fluid. The column is packed or internally coated with a selective adsorbent media. Individual chemicals in the analyte composition are differently soluble in the media within the column, and are able to pass through the column at different temperatures. The result is that as the temperature is raised, bands of individual chemical components from an analyte specimen are separated, traveling through the column at different rates.
The temperature of the column is eventually raised to a temperature that is sufficient to cause essentially all volatile components to pass through and elute from the column. The eluted compounds then flow into an ion trap detector, conventionally referred to as a mass spectrometer. The output from the gas chromatograph can provide an indication of the qualitative identity of each component of the composition, by comparing the elution times of the components to the elution times of known standards, as well as a quantitative indication providing a measure of concentration. However, the mass spectrometer provides a much more definitive qualitative identification of the chemicals, as well as a quantitative measurement.
This conventional method thus involves a complete sequence of sample injection, ramp heating to an elution temperature, followed by a clean-out period where the column is increased above the elution temperature, followed by cooling to the initial temperature, for each separate specimen to be analyzed. For urinalysis to determine MMA levels, this involves a 20-25-minute minimum cycle for each specimen, which ties up the analytical instrumentation and increases the cost of analysis.